Const (computer programming): Difference between revisions

Revision as of 19:13, 17 July 2024

Revision as of 02:30, 9 January 2025

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</syntaxhighlight>

However, in C neither of these is possible{{efn|In sinceC11 Cand doeslater not<code>_Generic</code> could have functionbeen overloading,used andto instead, this is handled by havingimplement a single function where the input is constant but the output isconst-correct writable:strchr.

<syntaxhighlight lang=c>char* strchr_m(char *s, int c);

char const* strchr_c(char const *s, int c);

#define strchr(X,Y) _Generic((X), \

char*: strchr_m, \

const char*: strchr_c \

)(X,Y)</syntaxhighlight>C23's actual solution does not use <code>_Generic</code> but is essentially equivalent.}} since C does not have function overloading, and instead, this is handled by having a single function where the input is constant but the output is writable:

<syntaxhighlight lang=cpp>

char *strchr(char const *s, int c);

</syntaxhighlight>

This allows idiomatic C code but does strip the const qualifier if the input actually was const-qualified, violating type safety. This solution was proposed by Ritchie and subsequently adopted. This difference is one of the failures of [[compatibility of C and C++]].